1. Field of the Invention
The present invention relates to a vehicle lamp used in vehicles, such as automobiles and the like, and to a method of determining a reflective surface of a reflector thereof.
2. Related Background Art
The vehicle lamps need to meet (1) the conditions from the aspect concerning the function as lamps and, in addition thereto, (2) the conditions from the aspect concerning the shape (shape constraints) and (3) the conditions from the aspect concerning the appearance (appearance constraints) because of their use in a mounted state on the vehicles such as the automobiles and the like. It is thus necessary to realize lamps optimized as to the conditions from the functional aspect while satisfying the given constraints from the shape aspect and the appearance aspect.
The conditions from the functional aspect include light uniformity with which the entire lamp lights uniformly, light diffusibility with which light is properly diffused to be observed from various directions, and so on, depending upon types of lamps.
As for the constraints from the vehicle and body side, the shape constraints include conditions defined by the volume and shape of lamp receiving portions of the body, the continuous shape of the outer surface of the lamp (the outer surface of lens) from the other body portions, and so on. The appearance constraints include conditions resulting from harmony with the appearance of the other body portions, requirements from the design aspect of the body, and so on.
With the recent trend toward fascinating styling of cars, there are increasing needs for vehicle lamps matching further various body-side constraints, according to forms of individual vehicles, types of lamps including illumination lamps, marker lamps, etc., and so on. An example of such lamps is a marker lamp that appears transparent and deep, because the lens forming the outer surface of the lamp is one with see-through nature.
An example of the conventional marker lamps of this type is a structure in which the reflective surface of the reflector for reflecting the light from the light source is formed in a unifocal paraboloid shape, the reflective surface is divided into an array pattern of segments, and the segments are provided with diffuse reflection steps for diffusely reflecting the light from the light source. In this case, since the light is diffused at the reflector, the lens does not have to diffuse the light much. As a consequence, the lens can be a stepped lens or a stepless lens with see-through nature, which realizes transparency as one of the appearance constraints described above.
In the case of the lamp in the above structure, however, the thickness of the lamp can not be decreased, because the basic shape of the reflective surface is based on a single paraboloid. It is thus difficult to match the lamp with the shape constraint of decrease in the depth of the lamp according to the volume of the lamp receiving portion of the body. In addition, it also fails to assure sufficient light uniformity of emitted light in the functional aspect.
Another marker lamp is one constructed in such structure that the basic shape of the reflective surface is a free-formed surface determined from the shape constraints and that a plurality of paraboloids of revolution are arranged in order in an approximately concentric circle pattern about the light source and the optical axis on the free-formed surface. In this case, it is relatively easy to meet the shape constraints including the decrease in the depth of the lamp, because the structure provides sufficiently large degrees of freedom in designing (for example, reference is made to Japanese Patent Application Laid-Open No. H09-33708).
In the above structure, however, the light reflected by the reflective surface is nearly parallel light without diffuse reflection, because the reflection employed is one by the paraboloids of revolution. In addition, it is necessary to diffuse the light with a fish-eye stepped lens or the like as the lens, and thus the lens lacks of the see-through nature, so as to fail to obtain the transparency as one of the appearance constraints.
The present invention has been accomplished in view of the above problems and an object of the present invention is thus to provide a vehicle lamp of thin shape and appearance with transparency while being improved in the functional conditions of light uniformity and light diffusibility, and provide a method of determining a reflective surface of a reflector in the vehicle lamp, which permits efficient determination of the shape of the reflective surface of the reflector capable of realizing the lamp satisfying such conditions.
In order to accomplish the above object, a method of determining a reflective surface of a reflector used in a vehicle lamp according to the present invention is a method comprising: (1) a condition setting step of setting a light source position at which a light source is to be placed, and an optical axis passing the light source position and defining a direction into which light from the light source is to be reflected by the reflector; (2) an initial reference line setting step of setting a plurality of initial reference lines each extending radially from a predetermined position on the optical axis so that on each of the initial reference lines luminous exitances M, specified in the direction along the optical axis for respective portions of the initial reference line, are constant; (3) a surface reference line creating step of creating a plurality of surface reference lines by deforming the plurality of initial reference lines so as to satisfy the condition of Mmax/Mminxe2x89xa66 as to a maximum Mmax and a minimum Mmin on the plurality of initial reference lines out of luminous exitances M for the respective, entire, initial reference lines, and a predetermined shape constraint; (4) a free-formed surface creating step of creating a free-formed surface comprising the plurality of surface reference lines; and (5) a reflective surface determining step of dividing the free-formed surface into an array of segments and assigning a reflective surface element having a diffuse reflection region for diffusely reflecting the light from the light source position, to each of the segments, thereby determining a reflective surface comprising a plurality of reflective surface elements.
Also, a vehicle lamp according to the present invention is a vehicle lamp comprising a light source, a reflector having a reflective surface comprising a plurality of reflective surface elements for reflecting light from the light source into a direction along a predetermined optical axis, and a lens which transmits the light reflected by the reflector, wherein the reflective surface is formed by assigning the reflective surface elements to respective segments obtained by dividing a free-formed surface satisfying a predetermined shape constraint, into an array pattern, and each of the plurality of reflective surface elements has a diffuse reflection region for diffusely reflecting the light from the light source, and wherein the free-formed surface satisfies the condition of Mmax/Mminxe2x89xa66 as to a maximum Mmax and a minimum Mmin out of luminous exitances M specified in the direction along the optical axis for respective portions on the free-formed surface.
Another vehicle lamp according to the present invention is a vehicle lamp comprising a light source, a reflector having a reflective surface comprising a plurality of reflective surface elements for reflecting light from the light source into a direction along a predetermined optical axis, and a lens which transmits the light reflected by the reflector, wherein the reflective surface is formed by assigning the reflective surface elements to respective segments obtained by dividing a free-formed surface satisfying a predetermined shape constraint, into an array pattern, and each of the plurality of reflective surface elements has a diffuse reflection region for diffusely reflecting the light from the light source, and wherein the reflective surface comprising the plurality of reflective surface elements satisfies the condition of Mmax/Mminxe2x89xa66 as to a maximum Mmax and a minimum Mmin out of luminous exitances M specified in the direction along the optical axis for respective portions on the reflective surface.
In order to realize the thin vehicle lamp with light uniformity and light diffusibility and with transparency and a deep look, it is necessary to provide the reflector with sufficient light diffusing capability and thereby relax the light diffusing capability required of the lens, thus permitting application of the lens with see-through nature, and to determine the shape of the reflective surface of the reflector so as to satisfy the conditions of light uniformity and light diffusibility and the condition of decrease in the depth of the lamp. The lens with see-through nature herein means a lens with low light diffusing capability through which the reflective surface of the reflector can be seen over a certain level; for example, a lens with diffuse steps for diffusing light only in one direction, and a lens without diffuse steps.
For determining the shape of this reflective surface, the above determining method employs the free-formed surface as the basic shape of the reflective surface instead of the paraboloid of revolution and thereby meets the condition of light uniformity out of the conditions from the functional aspect, and the condition of decrease in the depth as a shape constraint. Further, the method adopts the reflective surface elements formed in the respective segments obtained by dividing the free-formed surface into the array pattern, and thereby satisfies the condition of light diffusibility out of the conditions from the functional aspect, and the condition of transparency as an appearance constraint, thus determining the shape of the reflective surface for the lamp satisfying all the above conditions.
Particularly, the inventor discovered that the luminous exitance M in each part was extremely useful as an index for determination of the shape in order to improve the functional conditions of the lamp as to the shape of the reflective surface, particularly, the light uniformity. When the shape of the reflective surface is determined by applying values of the luminous exitance M for shape determination, deformation, etc. and properly setting the numerical range thereof, it becomes feasible to improve the condition of light uniformity, and compatibility between the light uniformity and the other conditions and to greatly increase the efficiency of the determining method and design steps.
The luminous exitance M herein is specified in the direction along the optical axis as described above and indicates quantity of luminous flux emitted per unit area (unit field area) in a view from the direction of the optical axis. A specific determination method of the luminous exitance is as follows. A reference plane is first defined as a plane normal to the optical axis, regions of unit areas on the reference plane are projected onto a curved surface of object (including a surface comprised of an assembly of plural curved surfaces) such as the free-formed surface or the reflective surface, and regions resulting from the projection are used as unit regions with respect to the optical axis on the curved surface. Then the luminous exitance M is defined as quantity of incident light from the light source into each of the unit regions. Since the quantity of incident light to each region is equal to quantity of light reflected and emitted from that region, the luminous exitance M defined as described above can be used as a suitable criterion for determining the quantity of reflected light from that region and the light uniformity in each part.
The reason why the luminous exitance M is defined as the quantity of light per unit area on the reference plane is that this reference plane is equivalent to the field where the lamp in an on state is observed from the optical-axis direction. Thus the light uniformity under practical use of the lamp can accurately be judged or adjusted from this luminous exitance M. The luminous exitance for each part (each segmental part of region) or the whole of the object is calculated by dividing the quantity of incident light to each part or to the entire region by the area on the reference plane to obtain the quantity of incident light per unit area.
Further, the inventor found out about the reflective surface determining method with attention to numerical distribution of luminous exitances M in respective parts, that it became feasible to efficiently and accurately determine the shape of the curved surface with improved light uniformity and light diffusibility while satisfying the various conditions, by use of a plurality of reference lines each extending radially from the optical axis.
Specifically, when a plurality of radial, initial reference lines are first set so as to make the luminous exitances M for the respective parts constant on each line, and when the free-formed surface is formed via the surface reference lines, based on the initial reference lines, the determining method can be simplified in the step of determining the shape of the reflective surface complying with the shape constraints including the decrease in the depth while satisfying the light uniformity.
For example, it is also possible to create the reference lines as a plurality of vertical curves and connect them in the lateral direction to form a curved surface. In view of the relation of the light source and the optical axis with the curved surface, use of such a method will complicate the procedures of determination of shape and result in failing to gain satisfactory characteristics. In contrast to it, the employment of radial reference lines facilitates the determining method and also improves the characteristics of the free-formed surface and the reflective surface obtained by this method. When the free-formed surface is created from the surface reference lines, it is desirable to create smooth free-formed curves from the respective surface reference lines so as to remove steps etc. on the surface, for example, by use of spline curves or the like.
Speaking here of realization of the preferred condition of Mmax/Mminxe2x89xa66 of the luminous exitances M for the entire reference lines, when this condition is applied to the luminous exitances M on the plurality of surface reference lines, conditions to substantially meet the condition of Mmax/Mminxe2x89xa66 can also be realized as to the luminous exitances M for the respective portions in the created free-formed surface and reflective surface. Alternatively, the shape of the reflective surface can also be determined by further imposing the above condition on the free-formed surface or on the reflective surface.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.